As the communications industry continues to evolve, ever-increasing demand for high-speed broadband solutions for communications will result, with the accompanying technologies experiencing a similar demand pattern. While industry analysts predict that 100-megabit speeds will be common by the year 2002, the disclosed antenna design can assist in delivering these speeds now.
The need for high-speed Internet access within the U.S. is well defined. With respect to Internet applications alone, as of December 1999, there were fewer than 250,000 U.S. customers purchasing DSL services, as compared to more than 30 million Internet customers. Beyond Internet applications, this novel antenna has a number of other uses for its special capabilities, including video, telephony and all forms of telephony, including mobile communications. This unique antenna design helps eliminates high infrastructure investment in constructing costly base stations, laying cable, or deploying satellites for high-speed Internet access by allowing more transceivers to be co-located on one tower.
This invention discloses a particular antenna design, which is referred to as a parabolic horn antenna. This antenna combines the familiar horn antenna, also known as a wave guide antenna, and the parabolic dish antenna The result is superior efficiency in terms of gathering captured radio energy and delivering that energy to the coaxial cable delivery system thus improving the speed of Internet access. When placed in an array it creates a high isolation antenna array useful when co-locating large numbers of transceivers at one location.
Just as radio equipment that is situated very close together can leak RF energy causing destructive interference, so can the antenna. Antennas are made to radiate energy as well as to collect the same sort of energy. Therefore it becomes very important, yet difficult, to isolate antennas so that when connected to multiple uncoordinated transmitters in close proximity the antennas will not interfere with each other. This is generally accomplished by two methods, the first is vectoring and the second is shielding. Vectoring is simply directing the RF energy that the antenna radiates into a desired direction. For high-speed wireless Internet access the need exists to direct the energy so efficiently that virtually no energy leaks to the antenna of another radio where it would be received by another nearby receiver. In essence, for this application, the antennas need to behave like very focused spotlights. In situations where few antennas are used, physical spacing between the antennas of 5 or more feet is possible, and, with the antennas directed into opposite directions, it is usually effective to simply use prior art directional antennas like the Breezecom model Uni-13, or similar models well known to those skilled in the art. Where the antenna density is higher, the design of this parabolic horn antenna delivers excellent isolation from other nearby antennas, even closely spaced and in the same relative vector.
The familiar horn antenna provides a means of coupling RF energy from a coaxial cable connection to free space by means of a radiator that is situated within the horn assembly. Reference the ("American Radio Relay League") Antenna Handbook, page 18-14, FIG. 19. The horn serves as an impedance matching device. The relative spacing of the radiator to the rear, inside surface will determine the impedance of the radiator, thus matching to the common 50-ohm coaxial RF cable. No attempt is generally made to focus the RF energy other than by the general dimensions of the horn that are calculated to fall within the guidelines of general wave guide design. Reference the ARRL Antenna Handbook, page 18-3, Wave Guide Dimensions, 1997-1998 American Radio Relay League.
The dimensions for typical wave guide antennas are determined by:
1. Cross sectional dimension, radius (r) being approximately 1/2 wavelength (wl) of frequency of operation (Fo) in a circular design when the device is operating in the Transverse Magnetic Mode (tm). PA1 2. Longest wavelength transmitted with little attenuation will be 3.2 r. PA1 3. Cutoff wl is 3.41 r. PA1 4. Shortest wl before next mode of operation (TE mode) becomes possible is 2.8 r. PA1 5. Spacing of radiator to rear wall is 1/4 wavelength/guide (wlg)
This invention acknowledges the effectiveness of the wave guide antenna, then improve upon it by adding additional geometry that focuses the RF energy upon the radiating element, thus increasing the energy incident upon the active element.
The parabolic shape of the closed end of the antenna focuses all of the captured RF energy onto the active radiator. This represents an improvement over traditional wave guide antennas with flat, closed ends. The prior art antennas reflect any uncaptured RF energy back out of the front of the antenna resulting in lost signal.
Horn antennas configured with reflectors are known in the prior art, but none with the configuration disclosed by this invention. For example U.S. Pat. No. 4,607,260 issued to Dragone on Aug. 19, 1986, titled Asymmetrically Configured Horn Antenna discloses a horn antenna which provides minimized cross-polarization in the far field of the antenna. The antenna arrangement comprises a horn including four walls wherein a first pair of opposing concentric conic walls are associated with a common longitudinal axis, and a second pair of opposing planar walls are aligned radially to the common longitudinal axis of the cones. The walls taper down from an offset parabolic main reflector to intersect a common apex corresponding to a focal point of the main reflector. The longitudinal axis of the horn is arranged at a predetermined angle to the common longitudinal axis of the cones to minimize cross-polarization in either one or both of the TE.sub.01 or TE.sub.10 modes in the far field of the antenna.
U.S. Pat. No. 2,817,837 issued to G. V. Dale et al on Dec. 24, 1957 discloses a large horn reflector described as a "sectorial bi-conical horn". There, the horn includes outwardly-concave, conically-shaped, front and rear surfaces and flat side surfaces. The horn arrangement is allegedly designed to provide improved impedance versus frequency characteristics along with substantially no tendency to become distorted by temperature changes.
Other horn antenna arrangements have been designed using a conical horn section as disclosed, for example, in U.S. Pat. No. 3,510,873 issued to S. Trevisan on May 5, 1970; U.S. Pat. No. 3,646,565 issued to G. P. Robinson, Jr. et al on Feb. 29, 1972; and U.S. Pat. No. 3,936,837 issued to H. P. Coleman on Feb. 3, 1976.
It is therefore clear that a primary object of this invention is to advance the art of antenna design. A more specific object is to advance said art by providing an improved efficiency antenna useful for high-speed wireless Internet access. It is a further object of this invention to provide an antenna with improved shielding and isolation that delivers improved isolation from other nearby antennas, even closely spaced and in the same relative vector.
These and other important objects, features, and advantages of the invention will become apparent as this description proceeds. The invention accordingly comprises the features of construction, combination of elements and arrangement of parts that will be exemplified in the construction hereinafter set forth, and the scope of the invention will be indicated in the claims.